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Front page first-timer EmLomBeeNo sends word of a 6.5-ton satellite that will soon be making a quick and fiery return to Earth. From Space.com:
"The huge Upper Atmosphere Research Satellite (UARS) is expected to re-enter Earth's atmosphere in an uncontrolled fall in late September or early October. Much of the spacecraft is expected to burn up during re-entry, but some pieces are expected to make it intact to the ground, NASA officials said. The U.S. space agency will be taking measures to inform the public about the pieces of the spacecraft that are expected to survive re-entry."
According to a NASA press conference today, you have a 1-in-21 trillion chance of being hit by falling debris. Who's feeling lucky?

Every day idiots all over the U.S. throw down $1 for a 1 in 100 million chance of winning some big jackpot lottery. So, on the off chance that said idiots stumble upon a news channel while channel-surfing between "The Jersey Shore" and Maury Povich's "Primetime Baby-Daddy Special" (and assuming that they're not too high to understand what's being said), there is a pretty good chance that they'll completely ignore the "1-in-21 trillion chance" addendum and only hear the "being hit by falling debris" part. In

Just look at Fukushima incident and the panicking idiots buying iodine in the US, China, Philippines, and elsewhere. Another example is spending hundreds of billions combating terrorism. They are worried about terrorists or nuclear plants while drink and driving or not worried about someone else killing them on the street.

People, including policy makers, are stupid and don't understand odds at all.

There was an article in the Washington Post this morning about people who are afraid to go to public events for fear of terrorist attack. I'm sure many of those very same people don't think twice about getting in a car.

I think that anyone who thinks there is a single "odds" for people on the earth being hit by this satellite doesn't understand orbital mechanics. Or even sub-orbital ballistics. (E.g. The further you are from the thrower, the lower your odds of being impaled by the lawn dart.)

If there's a 1 in 21 trillion chance that an individual will be hit, and there are 7 billion people, then the odds of someone, somewhere, getting hit are 21,000,000,000,000/7,000,000,000 or 1 in 3,000.

Of course, seeing as people tend to clump together, the most likely scenario, IF someone gets hit, is that multiple people get hit - so that is also ~ 1 in 3,000.

This matches pretty well with the actual odds in the article:

There is a 1-in-3,200 chance that a person somewhere on Earth could be hit by falli

A 300-pound piece of flaming satellite debris traveling at supersonic speeds is going to do more than hurt a little.

If it's something like a 300-pound crowbar, it would be wise to flee.

If it's a typical 300-pound random assortment of parts be supersonic as it re-enters the atmosphere, but by the time it gets to a few km from the surface in the much denser air it'll be very much subsonic. Still, I'm pretty sure I wouldn't want to be hit in the back of the head by it.

I suppose that you may feel superior to others, by way of you not having a McDonald's job, but no other person is any less human than you. And for those who don't get maths and probabilities, and share your infinite wisdom about such... well I bet that they're really nice down to earth people who'd help another human without thinking twice about it.

That's pretty dang high if you ask me. Especially for something that could have easily been prevented with a little foresight.

A little foresight and a big pile of tax money. You can be that the same people who are worried about a 1 in 3000 chance that someone somewhere will be hit are the some ones who think a 12 percent effective tax rate is too high. How much are you willing to spend to get rid of a 1 in 3000 chance that one of 7 billion people will get hit? Why wouldn't you be willing to use that money to buy and destroy guns?

It about a billion times more likely that some moron who either doesn't know how to turn of thei

What, you would rather an engineer AND a communications major be required to produce the press release, in order for it to change from "uncontrolled fall" to either "planned gravitationally-assisted descent process" (if you were told to spin it "for") and "massive, fiery man-made meteor raining death on unsuspecting victims" (if you were told to spin it "against")?

What, you would rather an engineer AND a communications major be required to produce the press release, in order for it to change from "uncontrolled fall" to either "planned gravitationally-assisted descent process" (if you were told to spin it "for") and "massive, fiery man-made meteor raining death on unsuspecting victims" (if you were told to spin it "against")?

Here's a link to the FOX News article [foxnews.com]. It says "Small risk to the public". That's paraphrased from the NASA press release that says "Extremely small risk to the public". So I guess that is some spin.

I think it means just that, but if you put that in perspective, there are much higher chances (almost sure) for somebody on Earth to be hit by a truck while sleeping in their bed (or add here any other improbable death)

Even worse! The Chinese satellite that got blasted a few years back is now 2317 traceable pieces. If the odds are for 1 piece, then odds are about 75% somebody is going to get thwacked!

Or maybe not.

Very much maybe not. That figure makes the assumption that none of the pieces will burn up on re-entry. Given that it's already in small pieces that will individually burn up more easily and that UARS is "huge" (I have no info on the Chinese ex-satellite, but let's assume for the moment that it was of fairly average size), the chances of being hit by a piece of that Chinese satellite are probably far lower.

If every individual has a 1 in 21 trillion chance, then the odds of everyone on the planet (assuming about 7 billion) "missing their chance" are approximately 2978/2979, or about 1:3000 that at least one person will get hit.

I imagine the 1 in 21 trillion is for "you" (an individual) getting hit, not for any individual getting hit.

Yes, but, the GP is right - if each person on the Earth has a 1 in 21 trillion chance of getting hit, then the chance that one of the roughly 7 billion people on this planet will get hit is right at 1 in 3000.

So apparently they used the remaining fuel a few years ago to move it into a more rapidly decaying orbit. If they had enough fuel to do that why not just deorbit the whole thing in a controlled fashion and aim it at an ocean? We've done that before. Obviously these are some very smart people but it seems weird that they'd have exactly enough fuel to put it into a rapidly decaying orbit but not enough fuel to handle that last little bit.

On the bright side, the danger from deorbiting satellites is pretty small. The biggest actual problem that has occurred when a Soviet satellite with radioactive material decided to scatter itself over a large part of Canada back in the 1970s http://en.wikipedia.org/wiki/Kosmos_954 [wikipedia.org]. When the US space station Skylab pulled a similar stunt over Australia, the local government fined NASA a few hundred dollars for littering.

Perhaps actually deorbiting in a controlled manner, aiming for a particular impact zone, would take more fuel than they had, but switching to a naturally decaying orbit for the same impact zone in a number of orbits time was doable?

According to TFA they used all its fuel just getting it into a lower orbit. It's a pretty large satellite, so I imagine even that probably took a lot of fuel. Also, it's been dead since 2005, so even the de-orbit took quite a while.

Well, the fact that it took years to de-orbit even after lowering the orbit suggests that they just ran out of fuel.

De-orbiting a satellite takes quite a bit of fuel, actually. I doubt that most carry that much. They are trying to carry enough to get the satellite into a low enough orbit that it eventually de-orbits, so that they aren't stuck up there forever. Things like geosync satellites don't have nearly enough fuel to do even that - you'd need something resembling the booster rocket that put it in o

Depending upon how high it was, that might have been several decades or even a millennium. You can be pretty sure that its batteries will be defunct and it's solar panels will be degraded to the point that its receiver and computer won't function.

Think of it this way, all orbital changes take energy. Now that is obvious but bear in mind that ALL orbital changes take energy. What I'm getting at is that the velocity for a satellite determines its altitude range (or just it's altitude in the case of a circular orbit).

Since any change in velocity takes energy (fuel) and the difference between an orbit that is 100% clear of the atmosphere is a vastly different energy than one that is mostly or all in it. Now, on the other hand if you intentionally make t

The biggest actual problem that has occurred when a Soviet satellite with radioactive material decided to scatter itself over a large part of Canada back in the 1970s http://en.wikipedia.org/wiki/Kosmos_954 [wikipedia.org]

The satellite
Was out of sight
Radioactive though
Quite all right
When it was highBut now it's very low.. [youtube.com]

In that case wouldn't it make more sense to use part of the fuel to put it into a decaying orbit and then use the last of it to do a controlled deorbit once gravity and friction had done most of the work?

Nice. I just read "Guards, Guards", where they mention this sort of logic. I haven't made it through all of his books yet. (man, there's a bunch!). My chances of reading them all, however, are a million- to-one.

I have read all that are at the local library (which I am pretty sure is almost all of them). Highly recommended: he is one of the funniest fantasy writers I have read in a long time, definitely up there with Douglas Adams (and possibly even a bit better; blasphemy, I know!).

I don't know how they calculate the odds, but 1 in 3500 is only twice as likely as you getting in a car accident. You also have to look at the number of incidents - we drive around with millions of cars and you have about 1 in 7000 chance to be in a car accident. There is 1 satellite falling and you have about 1 in 3500 chances of getting hit by it.

I think the odds are more than 1 in 21 trillion. The earth surface is 510,072,000 sq. km, 70% of that is water. This thing will probably destroy IF it hits land

Not sure how many are fans of dead like me, but the simple fact that she got nailed by a toilet seat comes to mind with this story.
Just be careful not to get hit, as you will be nicknamed toilet seat girl/boy for the remainder of your unlife.

I'm so glad that I took the time to skim the comments before posting because I had the same idea. For those of you who never saw the program, here's a link to the Wikipedia article on Dead Like Me. [wikipedia.org]

It's also on Netflix [netflix.com] as well as on Hulu [hulu.com]. Well worth watching; it's one of those that, like Firefly, got cancelled too early. They also did a movie later (made for TV, I think) that was pretty good.

How do they come up with that number? does that mean there are 21 trillion square whatevers of land that someone could possibly be standing? What if you are on a boat? what if you and 5 friends are on a boat is your boat 5 times more likely to get hit?
WE NEED THESE DETAILS!

How they say in the article that the satellite remains US property. Yeah okay, if their junk lands in my backyard (Canada) I think I'll keep it. Seriously how are they going to enforce that if it lands somewhere not in the US? I'm sorry but if your junk lands on some other countries soil they can do with it as they please.

Probably not. Odds are pretty good that the US and Canada have a treaty about that. Say an Air Canada jet had engine problems and landed at a private airport. Would it be okay for the owners of the airport to just keep it?The same treaties apply to in this case as say when a Russian pilot landed a Mig 25 in Japan. That plane was returned after it was inspected.... into little pieces.

Actually, many/most countries are signatory to the Space Treaty that specifically states (amongst other things) that any space debris landing on their territory has to be turned over to the country who launched it, if the latter wishes so. So yes: by international law, UARS remains US property.

In the first link in the summary, there are two images of the satellite--one against a backdrop of Earth and attached to a Space Shuttle manipulation boom. The next image is labeled as being the same thing except against a backdrop of deep space.

If so, then why are there clearly a wall, window and door in the darkened background of the second image? It appears to be a mock-up, or even possibly a scale-model, held in the air by the boom.

Didn't you ever see one of those cartoons where Wile E. Coyote tries to trick Roadrunner into eating iron shot so that he can then use a giant horseshoe magnet mounted on a car to catch him, but then somehow Wile E. Coyote ends up eating the shot and getting dragged all over the desert running into cacti as the car with the magnet careens uncontrollably about?

Interestingly the Ministry of Aviation in England did a study on something similar a while ago: http://aerade.cranfield.ac.uk/ara/arc/rm/3332.pdf [cranfield.ac.uk].
They claim that attitude deviations of up to 1.5 degrees may be observed for a 3 square metre surface area (normal to the Solar radiation) and a 2.5T satellite. That's not insignificant, and if the Sun did somehow produce a sudden large outburst, akin to a cataclysmic variable, then perhaps it might be enough to push the satellites into a decaying orbit. Then

Although note that attitude deviation is a rotational thing (whoops, should have noticed that) - the calculations are essentially to work out the torque on the satellite, not the change in orbit height. In which case it may well be very insignificant.

Yeah, I'm aware of those effects, as well as atmospheric extent expansion and contraction. That WILL affect satellites in the long run, but I can't see a major solar flare or CME causing it to rain debris all of a sudden.

That simple calculation doesn't consider geographic clustering of people. Since many people are clustered in large population centers that are outside of the predicted possible impact locations, you shouldn't include the entire world population in the reduction of personal odds to generalized odds. For instance, if it is predicted to impact the southern hemisphere, you could rule out all people except those on the African, South American, and Australian continents and islands south of the the equator.

Look at it this way. The number of meteorites that reach the surface of the earth is estimated at more than one per day. Most of them are very small, but none of them would fail to get your attention if they hit you. How many impacts on humans do you know of?

It's still right on average. Any increase in probability due to clustering of population in one place is accompanied with a decrease in probability elsewhere on the planet due to rarefaction of population.

No, it does not mean 1 in 3 chance someone is going to be hit, even by the wildest stretch of the imagination.

1 in 21 trillion is 4.7619047619047619047619047619048e-14

If we assume a world population of about 7 billion, and we fudge the math as 4.7619047619047619047619047619048e-14 * 7 billion, we get 1 in 3000 chance someone gets hit. I can only assume that you assumed a 7 trillion population and used this same incorrect math.

It is going to be a lot less than that in reality, but I can't be arsed to do the